A novel RPGR exon ORF15 mutation in a family with X-linked retinitis pigmentosa and Coats'-like exudative vasculopathy

PURPOSE

To describe the ophthalmic and genetic findings in a family with X-linked retinitis pigmentosa (RP) and Coats'-like exudative vasculopathy.

DESIGN

Observational case series.

METHODS

Family members underwent comprehensive ophthalmologic examination. Leukocyte genomic DNA samples were obtained and screened for RPGR (RP3) mutations by direct polymerase chain reaction sequencing.

RESULTS

The proband had RP with bilateral Coats'-like vasculopathy and was treated with fluorescein-potentiated argon laser therapy. The findings in two other affected male patients and three obligate carrier female patients were within the clinical spectrum of a typical X-linked-recessive RP. A novel nonsense RPGR exon ORF15 mutation (912G>T) was found to segregate with RP in this family.

CONCLUSIONS

This report expands the clinical heterogeneity spectrum caused by RPGR mutations and our knowledge concerning the molecular pathologic condition that pertains to Coats'-like RP. Consistent with the literature, Coats' response was not observed in all family members who were affected by RP, which suggests the involvement of other genetic and/or environmental factors.

Susceptibility genes for age-related maculopathy on chromosome 10q26

On the basis of genomewide linkage studies of families affected with age-related maculopathy (ARM), we previously identified a significant linkage peak on 10q26, which has been independently replicated by several groups. We performed a focused SNP genotyping study of our families and an additional control cohort. We identified a strong association signal overlying three genes, PLEKHA1, LOC387715, and PRSS11. All nonsynonymous SNPs in this critical region were genotyped, yielding a highly significant association (P < .00001) between PLEKHA1/LOC387715 and ARM. Although it is difficult to determine statistically which of these two genes is most important, SNPs in PLEKHA1 are more likely to account for the linkage signal in this region than are SNPs in LOC387715; thus, this gene and its alleles are implicated as an important risk factor for ARM. We also found weaker evidence supporting the possible involvement of the GRK5/RGS10 locus in ARM. These associations appear to be independent of the association of ARM with the Y402H allele of complement factor H, which has previously been reported as a major susceptibility factor for ARM. The combination of our analyses strongly implicates PLEKHA1/LOC387715 as primarily responsible for the evidence of linkage of ARM to the 10q26 locus and as a major contributor to ARM susceptibility. The association of either a single or a double copy of the high-risk allele within the PLEKHA1/LOC387715 locus accounts for an odds ratio of 5.0 (95% confidence interval 3.2-7.9) for ARM and a population attributable risk as high as 57%.

Meta-analysis of genome scans of age-related macular degeneration

A genetic contribution to the development of age-related macular degeneration (AMD) is well established. Several genome-wide linkage studies have identified a number of putative susceptibility loci for AMD but only a few of these regions have been replicated in independent studies. Here, we perform a meta-analysis of six AMD genome screens using the genome-scan meta-analysis method, which allows linkage results from several studies to be combined, providing greater power to identify regions that show only weak evidence for linkage in individual studies. Results from non-parametric analysis for a broad AMD clinical phenotype (including two studies with quantitative traits) were extracted. For each study, 120 genomic bins of approximately 30 cM were defined and ranked according to maximum evidence for linkage within each bin. Bin ranks were weighted according to study size and summed across all studies; the summed rank (SR) for each bin was assessed empirically for significance using permutation methods. A high SR indicates a region with consistent evidence for linkage across studies. The strongest evidence for an AMD susceptibility locus was found on chromosome 10q26 where genome-wide significant linkage was observed (P=0.00025). Several other regions met the empirical significance criteria for bins likely to contain linked loci including adjacent pairs of bins on chromosomes 1q, 2p, 3p and 16. Several of the regions identified here showed only weak evidence for linkage in the individual studies. These results will help prioritize regions for future positional and functional candidate gene studies in AMD.

Candidate gene analysis suggests a role for fatty acid biosynthesis and regulation of the complement system in the etiology of age-related maculopathy

Age-related maculopathy (ARM) is a leading cause of visual impairment in elderly Americans and is a complex genetic disorder. Hypothesized pathways for the etiology of ARM include cholesterol and lipoprotein metabolism and transport, extracellular matrix integrity, oxidative stress and inflammatory/immunologic processes. This study investigates 21 polymorphisms within 15 candidate genes whose products function within these pathways by performing family and case-control genetic association studies using clearly affected familial cases (n=338 families, 796 individuals), clearly affected, unrelated sporadic cases (n=196) and clearly unaffected, unrelated controls (n=120). Two genes demonstrated significant association with ARM status. A Met299Val variant in the elongation of very long chain fatty acids-like 4 (ELOVL4) gene was significantly associated with ARM in the case-control allele (P=0.001), case-control genotype (P=0.001) and case-control family (P<0.0001) tests. A Tyr402His variant in exon 9 in the complement factor H (CFH) gene was also significantly associated with ARM in the case-control allele (P<0.0001), case-control genotype (P<0.0001) and case-control family (P<0.0001) tests. All of these results remain significant after adjusting for false discovery rates to control for the impact of multiple testing. In addition, the CFH variant appears to play a role in exudative and atrophic disease, whereas the ELOVL4 variant may play a greater role in exudative disease in our population. These results support a potential role for multiple pathways in the etiology of ARM, including pathways involved with fatty acid biosynthesis and the complement system.

Histopathologic study of X-linked cone-rod dystrophy (CORDX1) caused by a mutation in the RPGR exon ORF15

PURPOSE

To evaluate the donor retina of a patient with X-linked cone-rod dystrophy caused by an RPGR exon ORF15 mutation.

DESIGN

Histopathologic study of the retina.

METHODS

The eye of a 69-year-old man was fixed at 1.6 hours postmortem and processed for histopathology and immunocytochemistry.

RESULTS

Grossly, the macula was atrophic with a bull's-eye appearance. The remaining retina showed postmortem edema but no intraretinal pigment. Microscopically, the macular retinal pigment epithelium was absent focally and had pigmentary changes elsewhere. Cones and rods were absent from the perifovea and reduced with shortened outer segments elsewhere in the macula. In the remainder of the retina, cones but not rods were reduced and all photoreceptor outer segments were shortened.

CONCLUSIONS

The abnormalities in both cone and rod photoreceptors confirm the importance of RPGR in both cell types but leaves unresolved how various exon ORF15 mutations lead to different clinical phenotypes.

A presumed missense mutation of RPGR causes abnormal RNA splicing with exon skipping

PURPOSE

A patient with retinitis pigmentosa demonstrated a novel RPGR mutation (213G>A, last base of exon 2) predicted to cause a missense change (G52R) in the final protein. This study was performed to determine whether this mutation altered the effectiveness of the adjacent splice site.

DESIGN

Observational case report.

METHODS

Total RNA was extracted from leukocytes of the proband and his carrier mother. Reverse transcription-polymerase chain reaction (RT-PCR) was performed by using the primers flanking exon 2 of RPGR transcript, followed by gel purification and direct sequencing.

RESULTS

Sequencing revealed skipping of exon 2 in the mutated transcript, leading to in-frame deletion of 42 amino acids affecting the critical RCC1-like domain.

CONCLUSIONS

The last base of exons is conserved as "G" in 80% of splicing consensus sequences, yet when changed, can completely disrupt constitutive splicing as in this patient. Our data confirm that the evaluation of the effects of some DNA sequence alterations at the RNA level might have important implications for appropriate genotype-phenotype correlations.

Age-related maculopathy: a genomewide scan with continued evidence of susceptibility loci within the 1q31, 10q26, and 17q25 regions

Age-related maculopathy (ARM), or age-related macular degeneration, is one of the most common causes of visual impairment in the elderly population of developed nations. In a combined analysis of two previous genomewide scans that included 391 families, containing up to 452 affected sib pairs, we found linkage evidence in four regions: 1q31, 9p13, 10q26, and 17q25. We now have added a third set of families and have performed an integrated analysis incorporating 530 families and up to 736 affected sib pairs. Under three diagnostic models, we have conducted linkage analyses using parametric (heterogeneity LOD [HLOD] scores under an autosomal dominant model) and nonparametric (Sall statistic) methods. There is ongoing evidence of susceptibility loci within the 1q31, 10q26, and 17q25 regions. If we treat the third set of families as a replication set, then two regions (10q26 and 17q25) are replicated, with LOD scores >1.0. If we pool all our data together, then four regions (1q31, 2q14.3, 10q26, and 17q25) show HLOD or Sall scores > or =2.0. Within the 1q31 region, we observed an HLOD of 2.72 (genomewide P=.061) under our least stringent diagnostic model, whereas the 17q25 region contained a maximal HLOD of 3.53 (genomewide P=.007) under our intermediate diagnostic model. We have evaluated our results with respect to the findings from several new independent genomewide linkage studies and also have completed ordered subset analyses (OSAs) with apolipoprotein E alleles, smoking history, and age at onset as stratifying covariates. The OSAs generate the interesting hypothesis that the effect of smoking on the risk of ARM is accentuated by a gene in the 10q26 region--a region implicated by four other studies.

Ordered subset linkage analysis supports a susceptibility locus for age-related macular degeneration on chromosome 16p12

BACKGROUND

Age-related macular degeneration (AMD) is a complex disorder that is responsible for the majority of central vision loss in older adults living in developed countries. Phenotypic and genetic heterogeneity complicate the analysis of genome-wide scans for AMD susceptibility loci. The ordered subset analysis (OSA) method is an approach for reducing heterogeneity, increasing statistical power for detecting linkage, and helping to define the most informative data set for follow-up analysis. OSA assesses the linkage evidence in subsets of potentially more homogeneous families by rank-ordering family-specific lod scores with respect to trait-associated covariates or phenotypic features. Here, we present results of incorporating five continuous covariates into our genome-wide linkage analysis of 389 microsatellite markers in 62 multiplex families: Body mass index (BMI), systolic (SBP) and diastolic (DBP) blood pressure, intraocular pressure (IOP), and pack-years of cigarette smoking. Chromosome-wide significance of increases in nonparametric multipoint lod scores in covariate-defined subsets relative to the overall sample was assessed by permutation.

RESULTS

Using a correction for testing multiple covariates, statistically significant lod score increases were observed for two chromosomal regions: 14q13 with a lod score of 3.2 in 28 families with average IOP </= 15.5 (p = 0.002), and 6q14 with a lod score of 1.6 in eight families with average BMI >/= 30.1 (p = 0.0004). On chromosome 16p12, nominally significant lod score increases (p </= 0.05), up to a lod score of 2.9 in 32 families, were observed with several covariate orderings. While less significant, this was the only region where linkage evidence was associated with multiple clinically meaningful covariates and the only nominally significant finding when analysis was restricted to advanced forms of AMD. Families with linkage to 16p12 had higher averages of SBP, IOP and BMI and were primarily affected with neovascular AMD. For all three regions, linkage signals at or very near the peak marker have previously been reported.

CONCLUSION

Our results suggest that a susceptibility gene on chromosome 16p12 may predispose to AMD, particularly to the neovascular form, and that further research into the previously suggested association of neovascular AMD and systemic hypertension is warranted.

A novel compound heterozygous mutation in the cellular retinaldehyde-binding protein gene (RLBP1) in a patient with retinitis punctata albescens

PURPOSE

To describe a patient with retinitis punctata albescens (RPA) associated with compound heterozygosity for two novel mutations in the RLBP1 encoding cellular retinaldehyde-binding protein (CRALBP).

DESIGN

Observational case report.

METHODS

The proband underwent a complete ophthalmic examination and leukocyte genomic DNA samples were obtained from him and his parents. The RLBP1 exons were analyzed by direct sequencing of PCR-amplified fragments.

RESULTS

The patient had a clinical phenotype suggestive of slowly progressive RPA, characterized by numerous yellow-white dots in the fundus. The RLBP1 sequence analysis revealed a novel compound heterozygotic mutation of Gly145Asp and Ile200Thr transmitted from the mother and father, respectively. Analysis of 100 control chromosomes showed no individuals with these sequence alterations.

CONCLUSIONS

Only eight RLBP1 mutations have been reported to date, and here we describe two novel mutations. These additional mutations will aid ongoing functional studies and add to our understanding of the molecular pathology pertaining to RLBP1-associated retinopathies.

The genetics of age-related macular degeneration

Age-related macular degeneration (ARM) is a progressive, chronic condition that results when the macula degenerates and central vision is lost. ARM is the leading cause of vision loss in Americans over age 50 and is a major public health concern. Very little is known about the etiology of ARM. Deciphering the genetic susceptibility associated with ARM holds great promise for gaining a better understanding of the disease, identifying at-risk individuals, and developing interventions and treatments.

Detection and assignment of mutations and minihaplotypes in human DNA using peptide mass signature genotyping (PMSG): application to the human RDS/peripherin gene

Peptide mass-signature genotyping (PMSG) is a scanning genotyping method that identifies mutations and polymorphisms by translating the sequence of interest in more than one reading frame and measuring the masses of the resulting peptides by mass spectrometry. PMSG was applied to the RDS/peripherin gene of 16 individuals from a family exhibiting autosomal dominant macular degeneration. The method revealed an A-->T transversion in the 5' splice site of intron 2 that is the likely cause of the disease. It also revealed four different minihaplotypes in exon 3 that represent particular combinations of SNPs at four different locations. This study demonstrates the utility of PMSG for identifying and characterizing point mutations and local minihaplotypes that are not readily analyzed by other approaches.

A new genetic locus for X linked progressive cone-rod dystrophy

X linked progressive cone-rod dystrophy (COD) is a retinal disease primarily affecting the cone photoreceptors. The disease is genetically heterogeneous and two loci, COD1 (Xp21.1-11.4) and COD2 (Xq27.2-28), have been previously identified. COD1 was recently shown to be caused by mutations in RPGR exon ORF15 (Xp21.1), the gene that is also responsible for RP3 type retinitis pigmentosa. In this study, we performed a linkage study to map the disease gene in a large Finnish family with X linked cone-rod dystrophy, using a panel of 39 X chromosomal markers. Several recombinations between the disease gene and markers in the Xp21.1-p11.4 region have excluded COD1 as a candidate locus in this family. Consistent with the linkage results, no mutation was detected by direct PCR sequencing of the coding region of RPGR, including exon ORF15. The COD2 locus has been also excluded as the site of the gene on the basis of negative lod score values obtained for COD2 linked markers. The disease causing gene of the studied COD family has been localised between the markers DXS10042 and DXS8060 on Xp11.4-q13.1. Positive pairwise lod scores >3 were obtained for markers DXS993, MAOB, DXS1055, and DXS1194. Since this locus is distinct from the previously identified two loci, COD1 and COD2, our results establish a new third genetic locus for X linked progressive cone-rod dystrophy and further expands our knowledge about the genetic heterogeneity underlying this disease entity.

Refinement of the physical location and the genomic characterization of the CRSP2 (EXLM1) gene on Xp11.4

In the course of our search for the gene responsible for X-linked cone-rod dystrophy (COD1), we constructed a physical map and contig (encompassing the region between DXS556 and DXS228), and identified sequences showing homologies to the expressed sequence tags (ESTs) that matched CRSP2 (EXLM1) transcript. We confirmed the expression of the CRSP2 gene in the retina and refined its exact genomic location between DXS1368 and DXS993. We demonstrated that the entire transcript is encoded within 31 exons. Primers were designed for mutation analysis of the exons by direct sequencing of PCR products from genomic DNA, and revealed no mutations in COD1 families. We subsequently excluded CRSP2 as a candidate for COD1 by demonstrating the causative mutations in the RPGR. However, due to its expression in different tissues and its contribution to transcriptional regulation, CRSP2 may be a candidate for other diseases that map to this region of the X chromosome.

Fluorescein-potentiated argon laser therapy improves symptoms and appearance of corneal neovascularization

PURPOSE

To evaluate patients' self-assessment of their symptoms and cosmetic appearance after fluorescein-potentiated argon laser treatment (FPAL) for corneal inflammation associated with neovascularization. To describe the objective effects of FPAL therapy on established corneal neovascularization with secondary corneal edema and lipid keratopathy.

METHODS

Fifteen patients with corneal neovascularization resulting from various infectious and traumatic etiologies were enrolled in an open, nonrandomized pilot study. Treatment consisted of repeated sessions of intravenous fluorescein, a photosensitizer, combined with blue-green argon laser applications to abnormal corneal vessels. Patients completed a written survey to grade their symptoms and cosmetic appearance prior to treatment and at the end of the follow-up period. Objective changes in signs after FPAL treatment were described by two nonmasked ophthalmologists after slit-lamp examinations and review of serial corneal photographs.

RESULTS

Clinical symptoms of blurred vision (p <or= 0.003), photophobia (p <or= 0.03), and cosmetic appearance ( p <or= 0.02) were found to be significantly improved by the patient's subjective assessment survey. There was a trend toward pain reduction (p <or= 0.06) but no apparent reduction in tearing or foreign body sensation (p <or= ns). Objective signs of corneal edema, neovascularization, and lipid keratopathy appeared to be reduced after FPAL therapy.

CONCLUSION

FPAL therapy for corneal neovascularization, edema, and lipid keratopathy resulted in a significant reduction in symptoms and improved quality of life for 14 of 15 (93%) patients. A controlled clinical trial to confirm the reported improvement in signs observed in this pilot study should be considered.

X-linked recessive atrophic macular degeneration from RPGR mutation

We mapped a new X-linked recessive atrophic macular degeneration locus to Xp21.1-p11.4 and show allelic involvement of the gene RPGR, which normally causes severe peripheral retinal degeneration leading to global blindness. Ten affected males whom we examined had primarily macular atrophy causing progressive loss of visual acuity with minimal peripheral visual impairment. One additional male showed extensive macular degeneration plus peripheral loss of retinal pigment epithelium and choriocapillaries. Full-field electroretinograms (ERGs) showed normal cone and rod responses in some affected males despite advanced macular degeneration, emphasizing the dissociation of atrophic macular degeneration from generalized cone degenerations, including X-linked cone dystrophy (COD1). The RPGR gene nonsense mutation G-->T at open reading frame (ORF)15+1164 cosegregated with the disease and may create a donor splice site. Identification of an RPGR mutation in atrophic maculardegeneration expands the phenotypic range associated with this gene and provides a new tool for the dissection of the relationship between clinically different retinal pathologies.

X-linked cone-rod dystrophy (locus COD1): identification of mutations in RPGR exon ORF15

X-linked cone-rod dystrophy (COD1) is a retinal disease that primarily affects the cone photoreceptors; the disease was originally mapped to a limited region of Xp11.4. We evaluated the three families from our original study with new markers and clinically reassessed all key recombinants; we determined that the critical intervals in families 2 and 3 overlapped the RP3 locus and that a status change (from affected to probably unaffected) of a key recombinant individual in family 1 also reassigned the disease locus to include RP3 as well. Mutation analysis of the entire RPGR coding region identified two different 2-nucleotide (nt) deletions in ORF15, in family 2 (delAG) and in families 1 and 3 (delGG), both of which result in a frameshift leading to altered amino acid structure and early termination. In addition, an independent individual with X-linked cone-rod dystrophy demonstrated a 1-nt insertion (insA) in ORF15. The presence of three distinct mutations associated with the same disease phenotype provides strong evidence that mutations in RPGR exon ORF15 are responsible for COD1. Genetic heterogeneity was observed in three other families, including the identification of an in-frame 12-nt deletion polymorphism in ORF15 that did not segregate with the disease in one of these families.

A tale of two genotypes: consistency between two high-throughput genotyping centers

Multiple genome-wide scans involving sib-pairs or limited pedigrees have been extensively used for a wide number of complex genetic conditions. Comparing data from two or more scans, as well as combining data, require an understanding of the sources of genotyping errors and data discrepancies. We have conducted two genome-wide scans for age-related maculopathy using the Center for Inherited Disease Research (CIDR) and the Mammalian Genotyping Service (MGS). Thirty individuals were typed in common, in order to allow for the alignment of alleles and comparison of the data sets. The analysis of these 8914 genotypes distributed over 321 markers in common demonstrated excellent agreement between these two laboratories, which have low rates of internal errors. Under the assumption that within each genotype, the smaller MGS allele should correspond to the smaller CIDR allele, the alleles align well between the two centers, with only a small fraction (less than 0.65%) of the aligned alleles showing large differences in sizes. However, since called allele sizes are integer "labels" which may not directly reflect the true underlying allele sizes, it is important to carefully prepare in advance if one wishes to merge data from different laboratories. In particular, it would not suffice to attempt to align alleles by typing only one or two controls in common. Fortunately, for the purposes of linkage analysis, one can avoid merging difficulties by simply carrying out linkage analyses using laboratory-specific allele labels and allele frequencies for each laboratory-specific subset of the data.

Age-related maculopathy: an expanded genome-wide scan with evidence of susceptibility loci within the 1q31 and 17q25 regions

PURPOSE

We seek to identify genetic loci that contribute to age-related maculopathy susceptibility.

METHODS

Families consisting of at least two siblings affected by age-related maculopathy were ascertained using eye care records and fundus photographs. Additional family members were used to increase the power to detect linkage. Microsatellite genotyping was conducted by the National Heart, Lung and Blood Institute Mammalian Genotyping Service and the National Institutes of Health Center for Inherited Disease Research. Linkage analyses were conducted with parametric (autosomal dominant; heterogeneity lod score) and nonparametric methods (S(all) statistic) using three diagnostic models. False-positive rates were determined from simulations using actual pedigrees and genotyping data.

RESULTS

Under our least stringent diagnostic model, model C, 860 affected individuals from 391 families (452 sib pairs) were genotyped. Sixty-five percent of the affected individuals had evidence of exudative disease. Four regions, 1q31, 9p13, 10q26, and 17q25, showed multipoint heterogeneity lod scores or S(all) scores of 2.0 or greater (under at least one model). Under our most stringent diagnostic model, model A, the 1q31 heterogeneity lod score was 2.46 between D1S1660 and D1S1647. Under model C, the 17q25 heterogeneity lod score at D17S928 was 3.16. Using a threshold of 1.5, additional loci on chromosomes 2 and 12 were identified.

CONCLUSIONS

The locus on chromosome 1q31 independently confirms a report by Klein and associates mapping an age-related maculopathy susceptibility gene to this region. Simulations indicate that the 1q31 and 17q25 loci are unlikely to be false positives. There was no evidence that other known macular or retinal dystrophy candidate gene regions are major contributors to the genetics of age-related maculopathy.

Identification, genomic structure, and screening of the vacuolar proton-ATPase membrane sector-associated protein M8-9 gene within the COD1 critical region (Xp11.4)

PURPOSE

Our goal is to identify the gene responsible for X-linked cone-rod dystrophy (COD1) that has been localized to a limited region of Xp11.4.

METHODS

A complete physical contig of the COD1 region was partially sequenced and subjected to BLAST searches to identify homologies with GenBank ESTs. ESTs were analyzed for overlapping or related cDNA sequences and retinal expression by PCR screening of multiple human retina cDNA libraries. RACE was performed to complete the missing 5' end of the transcripts. Transcripts were compared with genomic sequences to specify intron-exon boundaries. Genomic DNAs from COD1-affected males from 3 families were screened for mutations using direct PCR sequencing of the exons.

RESULTS

The vacuolar proton-ATPase membrane sector-associated protein M8-9 (APT6M8-9) gene was identified within our critical region. We confirmed its retinal expression and its genomic location in our physical contig. Eight exons (with flanking intronic sequences) were characterized from partial cDNA sequence and genomic sequence data. An additional 5' end exon was identified using RACE. No mutations were found in the COD1-affected males.

CONCLUSIONS

The combination of disease mapping and information from the Human Genome project has enabled us to identify candidate genes within the COD1 region, including APT6M8-9 gene. We found no evidence that this gene is responsible for COD1 in our families, but it may be an important candidate for other diseases that have been mapped to this region of the X chromosome.

Concentric retinitis pigmentosa: clinicopathologic correlations

Progressive concentric (centripetal) loss of vision is one pattern of visual field loss in retinitis pigmentosa. This study provides the first clinicopathologic correlations for this form of retinitis pigmentosa. A family with autosomal dominant concentric retinitis pigmentosa was examined clinically and with visual function tests. A post-mortem eye of an affected 94 year old family member was processed for histopathology and immunocytochemistry with retinal cell specific antibodies. Unrelated simplex/multiplex patients with concentric retinitis pigmentosa were also examined. Affected family members of the eye donor and patients from the other families had prominent peripheral pigmentary retinopathy with more normal appearing central retina, good visual acuity, concentric field loss, normal or near normal rod and cone sensitivity within the preserved visual field, and reduced rod and cone electroretinograms. The eye donor, at age 90, had good acuity and function in a central island. Grossly, the central region of the donor retina appeared thinned but otherwise normal, while the far periphery contained heavy bone spicule pigment. Microscopically the central retina showed photoreceptor outer segment shortening and some photoreceptor cell loss. The mid periphery had a sharp line of demarcation where more central photoreceptors were near normal except for very short outer segments and peripheral photoreceptors were absent. Rods and cones showed abrupt loss of outer segments and cell death at this interface. It is concluded that concentric retinitis pigmentosa is a rare but recognizable phenotype with slowly progressive photoreceptor death from the far periphery toward the central retina. The disease is retina-wide but shows regional variation in severity of degeneration; photoreceptor death is severe in the peripheral retina with an abrupt edge between viable and degenerate photoreceptors. Peripheral to central gradients of unknown retinal molecule(s) may be defective or modify photoreceptor degeneration in concentric retinitis pigmentosa.

Genetic heterogeneity of Usher syndrome: analysis of 151 families with Usher type I

Usher syndrome type I is an autosomal recessive disorder marked by hearing loss, vestibular areflexia, and retinitis pigmentosa. Six Usher I genetic subtypes at loci USH1A-USH1F have been reported. The MYO7A gene is responsible for USH1B, the most common subtype. In our analysis, 151 families with Usher I were screened by linkage and mutation analysis. MYO7A mutations were identified in 64 families with Usher I. Of the remaining 87 families, who were negative for MYO7A mutations, 54 were informative for linkage analysis and were screened with the remaining USH1 loci markers. Results of linkage and heterogeneity analyses showed no evidence of Usher types Ia or Ie. However, one maximum LOD score was observed lying within the USH1D region. Two lesser peak LOD scores were observed outside and between the putative regions for USH1D and USH1F, on chromosome 10. A HOMOG chi(2)((1)) plot shows evidence of heterogeneity across the USH1D, USH1F, and intervening regions. These results provide conclusive evidence that the second-most-common subtype of Usher I is due to genes on chromosome 10, and they confirm the existence of one Usher I gene in the previously defined USH1D region, as well as providing evidence for a second, and possibly a third, gene in the 10p/q region.